On 11 Oct 1999, Andreas J. Koenig wrote:
> Date: 11 Oct 1999 12:48:54 +0200
> From: "Andreas J. Koenig" <[EMAIL PROTECTED]>
> To: Oleg Bartunov <[EMAIL PROTECTED]>
> Cc: [EMAIL PROTECTED], [EMAIL PROTECTED]
> Subject: Re: http headers for cache-friendly modperl site
>
> >>>>> On Mon, 11 Oct 1999 13:18:12 +0400 (MSD), Oleg Bartunov <[EMAIL PROTECTED]> said:
>
> > 1. Do you have some examples on-line to illustrate
> > cache-friendly dynamical pages ?
>
> On www.stadtplandienst.de the headers for the graphics have optimal
> headers, I think. The headers for HTML could be improved though.
>
> On the other machines where I have prepared everything to be
> cache-friendly, I yet have to decide about a good expiration schedule.
> And as often, without a pressing need, I haven't yet come around to
> finetune it.
Thanks for references. I could recommend also mailing list archive
http://www.progressive-comp.com/Lists/ which is cache-friendly
with dynamic content site. Also is very useful.
>
> > 2. I'm building server with fully dynamic content using
> > Apache, modperl and HTML::Mason and would like to implement
> > cache-friendly strategy you described. But I have some problem:
> > In Russia we have several encodings for russian language
> > ( koi8-r - mostly Unix, win-1251 - mostly windows and several
> > others). Documents generated in native server's encoding and
> > translated to another encoding on-fly depending on several
> > parameters (user directly specify port number for example or
> > server understand on some logic (by User Agent string for example) what
> > encoding would be the best for user). If user directly selected
> > port number URL would changed, say http://some.host:8100/ for koi8-r
> > and http://some.host:8101/ for win-1251. In such situation there
> > are no problem with caching on proxy servers because URL's are different.
> > But in case when server automagically recognize encoding of client
> > URL stays the same for differnet encodings - just http://some.host/
> > and this cause a trouble with proxy. Suppose if user1 from windows machine
> > and user2 from Unix request the same document using the same proxy.
>
> This is exactly the same problem for any content negotiation. If you
> are using content negotiation, you *must* specify the Vary header as
> described in my document. But as soon as you have a Vary header, you
> are out of luck with regard to caching proxies because squid is unable
> to cache documents with a Vary header (it just expires them
> immediately) and I believe there is no other Proxy available that does
> handle Vary headers intelligenty. So although you are acting
> cache-friendly and correct, the current available cache technology
> isn't up to the task.
>
> But as a workaround you can and should work with a redirect.
>
> 1. Decide about a parameter in the querystring or in the pathinfo or
> in the path that codifies everything you would normally handle by
> interpreting an incoming header, like Accept, Accept-Encoding,
> Accept-Charset, User-Agent, etc.
>
> 2. As one of the first things your program should check for the
> precense of this parameter in the requested URI.
>
> 3. If it is there, you have a unique URI and can answer in a
> cache-friendly way. If it isn't there, you code it into the
> received URI and answer with a redirect to the URI you just
> constructed.
Yes,
I already found workaround to generate unique URL (using different port number)
and it works quite fine. There were some problems in 2 servers setup
(it's easy to get redirection loop) but I found a right way.
Thanks for help,
Oleg
>
> An example: www.meta-list.net, where we roughly do the following,
> where $mgr is an Apache::HeavyCGI object we created earlier and $cgi
> is an Apache::Request object.
>
> my $acc = $cgi->param('acc');
>
> if (defined($acc)) {
> my $lang;
> ($mgr->{CAN_UTF8},$mgr->{CAN_GZIP},$mgr->{CAN_PNG},$mgr->{Lang}) =
> unpack "a a a a*", $acc;
> } else {
> my $utf8 = $mgr->can_utf8;
> my $gzip = $mgr->can_gzip;
> my $png = $mgr->can_png;
> my $lang = $r->header_in("Accept-Language");
> my $param = $utf8 . $gzip . $png . $mgr->uri_escape($lang);
> my $redir_to;
> if ($r->method_number == M_GET) {
> my $args = $r->args;
> $redir_to = $mgr->myurl . "?acc=$param";
> $redir_to .= "&$args" if $args;
> } elsif ($r->method_number == M_POST) {
> warn "We got a POST but we are only prepared for GET!";
> return;
> }
> $r->header_out("Location",$redir_to);
> require Apache::Constants;
> my $stat = Apache::Constants::REDIRECT();
> $r->status($stat);
> $r->send_http_header;
> }
>
> This code doesn't work exactly as posted because I simplified a few
> things to illustrate the point, but I hope it helps clarify things.
>
> --
> andreas
>
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: [EMAIL PROTECTED], http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83
